The proposd research involves glucocorticoid receptors in normal and malignant rodent and human tissues, e.g. normal rat kidney, a transplantable line of mouse mammary tumors, and human leukemic lymphocytes. The specific aims include: 1) analyses of the mechanisms of receptor stabilization by leupeptin and other protease inhibitors, 2) characterization and purification of the intact, stabilized receptors, 3) identification and purification of the enzymes responsible for receptor cleavage in extracts of various target tissues, 4) treatment of purified receptors with the purified enzymes and characterization of the cleavage products, and 5) further studies of receptor modification by treatment with ribonuclease. The techniques will include chromatography on Sephadex LH-20, ion exchange resins and Agarose gels of various porosities, density gradient centrifugation and assays of proteolytic activity using flurorogenic substrates and 125I-fibrin plates. The results should contribute to our understanding of the native structure of cytoplasmic steroid receptors, the possible effects of steroid binding on receptor conformation, and the mechanism of in vitro activation of receptors for interaction with nuclear components, and should facilitate the eventual purification of intact receptors from these and other target tissues.